Blood-brain barrier (BBB) is an important structure consisting of brain microvessel endothelial cell and a basement membrane closely connected thereto and astrocyte foot processes around the blood vessels. A main function thereof is to maintain stability of an environment in a central nervous system and a normal function of neuron. The brain microvessel endothelial cell is to some extent distinct from endothelial cells of other blood vessels of an organism in terms of gene constitution and morphological structure, and on its cell membrane are distributed various protein and transporters maintaining its special selective permeability.
The capability of a drug penetrating BBB is usually related to relative molecular mass, fat solubility, charge property of the drug itself and its bonding capability with plasma protein and a special carriers or receptor transport system. In addition to water, electrolyte and partial macromolecular substances which may pass freely, most drugs (such as levodopa, codein etc.) that may penetrate the BBB are transported into brain via vector mediation. Its mechanism comprises facilitated diffusion, active transport and pinocytosis. It is difficult for hydrophilic and macromolecular drugs themselves to penetrate the BBB. Some lipophilic drugs with suitable molecular weight can penetrate the BBB, but they are apt to be transported by an efflux pump by P glycoprotin (P-gp) on the BBB so that effective drugs in the brain have a low concentration and act in a short time period.
Many drugs have a very good efficacy, but the high blood-brain barrier permeability causes large toxicity and side effects to the central nervous system. Upon studying these drugs, main thoughts are given to reduction of the blood-brain barrier permeability as well as maintenance or improvement of drug efficacy. There are many methods of reducing the blood-brain barrier permeability. The present invention reduces the blood-brain barrier permeability and achieves an effect of reducing toxicity and side effects and maintaining activity mainly by modifying polyethylene glycol, introducing low molecular weight polyethylene glycol into the compound structure to increase its hydrophilicity.
Polyethylene glycol (PEG) modification technology is a new drug delivery technology which has developed rapidly in recent years and is a technology linking activated polyethylene glycol to a drug molecule or surface. After combining with the polyethylene glycol, pharmacokinetics of the drug changes and thereby pharmacodynamics changes so that the drug in vivo activity is improved. At present, polyethylene glycol (PEG) technology has already been extensively applied to modification of protein drugs and becomes an important means for improving clinical effects of the protein drugs. Currently, there are eleven polyethylene glycol drug products in the international market, wherein annual sales amount of PEG-intron®, PEGasys®, Neulasta® or Macugen® exceeds 100 million US dollars, and annual sales amount of PEGasys® and Neulasta® is 1.8 billion US dollars and 3.6 billion US dollars respectively. In recent years, polyethylene glycol (PEG) modification technology has already spread from protein drugs to small molecule drugs. Small molecules of the drugs, after being modified by polyethylene glycol, mainly have the following advantages: 1) increase drug water-solubility; 2) change oil-water distribution coefficient; 3) prolong cyclic half-life of the drug, reduce times of administration, improve patient compliance and life quality and reduce treatment fees; 4) reduce enzyme degradation and improve bioavailability. However, generally, in vitro activity of the drug after polyethylene glycol (PEG) modification substantially reduces. For example, the activity of PEGasys® in vitro is only about 2 percent of interferon. While using advantages of polyethylene glycol (PEG) modification (e.g., increase water-solubility and reduce blood-brain barrier permeability), maintaining or improving the bioactivity of the drug in vitro is a problem of polyethylene glycol (PEG) modification technology need to be solved urgently,
Meanwhile, most drugs effect by interacting with a specific receptor in vivo and changing physiological and biochemical function of cells. Currently, there are tens of already-determined receptors, wherein functions of cells of a majority of organisms are all identified by membrane receptors, and wherein main membrane receptors belong to G Protein-Coupled Receptor (GPCR) family. It is believed that GPCR exists mainly in the form of a monomer, which is coupled to G protein to produce identification of a ligand and mediate conduction of a series of signals. In recent years, research of GPCR indicates that GPCR may exist in the form of a dimer and a polymer. For example, opium receptor, β2AR, dopamine receptor, chemotactic factor receptor, mGluR5, extracellular Ca2+ sensitive receptor all can form a dimer and polymer. The dimer comprises homodimer and heterodimer. FIG. 1 shows a 3-D structure of a heterodimer of Mu-delta opioid peptide receptor.
In consideration with reduction of blood-brain barrier permeability and inspiration of receptor dimers and polymers, we designed a class of compounds with a new structure by using properties of small-molecule polyethylene glycol, with the reference to the double group structure of the natural antibody in organism. Said compounds are characterized in that an end of small-molecule polyethylene glycol is combined with two more drug molecules in the form of a chemical bond to form a double-group or multi-group structure of a similar antibody. Hydrophilicity of oxygen atoms in polyethylene glycol fragments and space flexibility of linear-chained alkoxy increases possibility of the new compounds binding with the receptor dimer or multimer and improves drug activity; meanwhile, as molecular weight increases, hydrophilicity increases, in vivo distribution changes, blood-brain barrier permeability of the drug falls, and the side effects to the central system decrease. Furthermore, introduction of small-molecule polyethylene glycol causes changes of the oil-water distribution coefficient of the new compounds and increase of water-solubility, some drugs that cannot be taken orally can be produced as oral drugs.
In early-stage experimental research of the laboratory, Patent CN201110393196.1 disclosed a method of low molecular weight polyethylene glycol to combine with tamsulosin by chemical bond. Patent US2005136031A1 disclosed a method of linking polyethylene glycol having one closed end with naloxone. Patent CN201210040133.2 disclosed a method of linking naloxone with low molecular weight polyethylene glycol. Pharmacological results testify that activity of a product produced by linking both ends of polyethylene glycol with naloxone is higher than an single-end substitution product. However, the above work all does not carry out sufficient research for the blood-brain barrier permeability of this series of compounds.
The present invention provides a new polyethylene glycol modified drug. The polyethylene glycol modified drug is polyethylene glycol-linked drug dimer or polymer, which is obtained by the method of deriving end groups of low molecular weight polyethylene glycol having two or more end groups, and combining them with the drug molecules. The new compounds exhibit increased drug activities in vitro, increase of solubilities, changes of oil-water distribution coefficient, changes of distribution in vivo, reduction of blood-brain barrier permeability and finally rise of the effect in vivo.